1. Technical Field
The present invention relates to expansion dowel systems. More particularly, the present invention relates to construction joints for transferring stresses across a joint between concrete constructions. More particularly, the present invention relates to the use of polymeric sleeves extending around a portion of a rigid dowel bar within the concrete construction.
2. Description of Related Art
Concrete responds to changes in temperature and moisture when movement associated with these changes (or for other reasons such as internal chemical reaction) is restrained. In these instances, stresses develop that can lead to cracking. To control cracking, joints are built at interval distances short enough to maintain stresses below critical values. Transverse joints are saw cut, placed through induced cracking, or formed at pre-determined spacings.
Concrete pavements for highways, airport runways and the like are generally placed in strips or lanes with a longitudinal joint formed between adjacent strips or lanes. Concrete is poured in the first strip and allowed to cure. Subsequently, concrete is poured and cured in the adjacent strip and so on until the concrete pavement is completed. A longitudinal joint is formed between adjacent strips to facilitate construction and to reduce stresses and control cracking caused by contraction or expansion of the concrete. Transverse or slug joints are also formed in concrete by cutting or sawing the concrete at a given location and to a given depth.
Similarly, joints are formed in concrete structural slabs, walls, footings and the like to minimize stresses and/or simplify construction methods. Of these joints, there are several types. For example, the expansion joint provides a space between slabs to allow for expansion or swelling of the slab as temperature and moisture increase or grow occurs. A construction joint provides a finished edge or end so that construction operations interrupted for some length of time may be continued or resumed without serious structural penalty.
Load is transferred across a joint principally by shear. Some bending moment may be transferred across the joints through tie joints. Good load transfer capability must be built into the joint or the load carrying ability of the concrete slab or structure will be reduced. The alternative is to strengthen the concrete by improving support or increasing depth to minimize the joint load transfer weakness.
Tie bars and dowels are often used in concrete design to improve load transfer at the joint between concrete slabs or structures. Such tie bars and dowels are embedded in the concrete and arranged across the joint in a direction substantially perpendicular to the axis defined by the joint. Various approaches, depending on the type of tie bar or dowel, have been suggested with respect to concrete construction joints.
In the construction of concrete slabs on grade, it is common practice to install continuous side forms with dowels for future adjacent slab concrete placement and to place concrete in long continuous strips. It is also known to place slab dowels and sleeves at specified distances across the strips to allow the strips to have a controlled plane to accommodate shrinkage of the concrete. The positions of these dowel locations are marked on the side forms and the concrete after placement and finishing is struck to provide a joint at these locations.
The functions of the tie bars and dowels are to keep contiguous sections of concrete in alignment during contraction and expansion, and to transfer shear stresses and bending moments across the joint between the two slabs.
FIG. 1 shows a typical dowel bar sleeve assembly which is used in a concrete structure. As depicted in FIG. 1, sleeve dowel bar assemblies are embedded in the first concrete slabs, and arranged across the transverse transfer joint 22a to 22e and 23a to 23e, in a direction substantially perpendicular to the axes defined by the transverse transfer joint. Similarly, dowel sleeves are embedded in the first concrete slabs and arranged across the joint in a direction substantially perpendicular to the axes defined by the longitudinal transfer joint 24a to 28a, etc. In a typical installation sleeve, dowel bar assembly 32 is positioned on the rebar-matrix and the concrete slab is poured. The concrete slab is allowed to harden in situ with the dowel bars and dowel sleeves embedded therein.
After the first concrete slab has undergone expansion or contraction from thermal or drying shrinkage, the second concrete slab is placed adjacent to the first concrete slab after the dowel bars are inserted into the sleeves previously placed in the prior concrete pour so that the dowel bars are also essentially embedded in the second concrete slabs. The second concrete slab will attempt to shrink during curing in a similar manner to the shrinkage of the first concrete slab.
In a conventional installation, the dowel bars arranged across longitudinal joints between the first and second concrete slabs will attempt to restrain the second concrete slabs from movement. The developed and internal stress in the second concrete slab can create an added stress which may cause cracking by itself or when added to an applied load upon the slabs. The cracks will often develop along a line near the ends of the dowels bars. Referring now to FIG. 1, an illustrative reinforced concrete slab section 10 is shown which includes two versions of the concrete dowel slab joint system in place of the conventional dowel bars previously discussed. In a first version, denoted 18, a dowel bar 20 is positioned within a single sleeve body 32. This first version is used to bridge longitudinal joints, for example, the joints formed between adjacent slab segments 12a, 14a, 16a, etc. In a second version, denoted 19, a dowel bar 20 is positioned within the confines of a pair of sleeves 32. The second version is employed to bridge transverse joints 22a, 22b, 22c, etc. A reinforced concrete slab section 10 comprises a concrete slab and may include an interconnected matrix of reinforcing re-bar rods (not shown). The matrix of reinforcing re-bar rods are arranged in a predetermined pattern according to known principals of structural engineering.
In the past, various U.S. patents have issued relating to such expansion dowel systems. In particular, U.S. Pat. No. 5,797,231, issued on Aug. 25, 1998 to D.R. Kramer, describes a concrete dowel slab joint system for maintaining adjacent sections of concrete, and alignment during contraction and expansion of the concrete, and for transferring shear stresses and bending moments across a joint formed between adjacent concrete slabs. This system includes a sleeve assembly for receiving and maintaining the dowel bar there within. As a result, the dowel bar will not transmit substantial shear stresses to the concrete during the contraction and expansion of the concrete. The sleeve assembly comprises an elongate sleeve body having an outer surface and an inner surface and defines a hollow interior compartment. The sleeve assembly uses a collapsible spacer member located within the hollow interior compartment.
U.S. Pat. No. 5,628,579, issued on May 13, 1997 to H. Forrester, describes an expansion dowel which includes an expansion sleeve and an expanding member. The expansion sleeve is provided with a bore tapering in the setting direction as well as with an open ended longitudinal slot. The expanding member has a blind bore open towards the setting side and has a lug projecting from the same at its opposite end. The cross-sections of the lug and the blind bore are matched to one another so that a rated break point or failure point is formed.
U.S. Pat. No. 5,931,619, issued Aug. 3, 1999 to M. Hartmann, describes an expansion dowel formed of an axially extending expansion sleeve with a through bore and an expansion region having at least one axially extending slot, and an expanding member axially displaceable by axially directed blows in the through bore from an initial position to an end position in which the expansion region is expanded The through bore has an inside surface of the expansion region adjacent to an envelope or outside surface of the expanding member in the end position with radius of curvature of the inside surface being basically the same as the radii of curvature of the envelope surface of the expanding member.
Conventionally, the prior art dowel bar sleeves are formed of a single tubular member, such as those sold by Shepler""s. The plastic tubing used for these dowel sleeves is cut to the desired size, and then the open end of the tube is stapled together. It has been found that stapling of the end of the dowel sleeve will not prevent water intrusion into the interior of the sleeve. Often, this stapling is difficult to perform and will inadequately secure the end of the tube together. The stapling requires a manual operation which requires expensive labor to complete. Alternatively, the tube is provided with a cap. The cap must be injected molded so as to properly fit the end of the tube. The injection molding of the cap is a relatively expensive procedure. Often, the cap will not properly fit the end of the tube. In other circumstances, the cap will be improperly assembled on the end of the sleeve so that liquid intrusion can occur.
It is an object of the present invention to provide a sleeve for a dowel bar which is relatively inexpensive.
It is another object of the present invention to provide a sleeve for a dowel bar which prevents water intrusion into the interior of the sleeve.
It is still a further object of the present invention to provide an expansion dowel system whereby the dowel bar is centered within the interior of the sleeve.
It is still a further object of the present invention to provide an expansion dowel system which is easy to use and requires no assembly.
It is still a further object of the present invention to provide an expansion dowel system which minimizes the possibility of human error during installation.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.
The present invention is an expansion dowel system comprising a dowel bar and a polymeric sleeve affixed over the dowel bar. This sleeve has a closed end and an open end. The closed end is heat sealed and liquid tight. The sleeve has a tubular portion extending to the open end. The sleeve has a tapered portion extending to the closed end. The tapered portion has a first flat surface and a second flat surface heat sealed together at the closed end. The tapered portion has a narrowing interior extending from the tubular portion to the closed end.
The dowel bar has an end abutting the narrowing interior of the tapered portion. The dowel bar extends centrally through the sleeve and is generally spaced from an interior wall of the sleeve. The dowel bar has an end extending outwardly of the open end of the sleeve.
A first pour of concrete extends over and around the sleeve. The dowel bar has an end extending outwardly of the first pour of concrete. A second pour of concrete is adjacent to the first pour of concrete. The end of the dowel bar extends into this second pour of concrete. The second pour of concrete has an edge extending in parallel relationship to an edge of the first pour of concrete. The dowel bar on the sleeve extends transverse to these edges. Each of the first and second pours of concrete are placed upon an underlying surface. A chair is positioned on the underlying surface and extends upwardly therefrom. The sleeve is secured to a top surface of the chair.
The present invention is also a method of forming a sleeve used with the dowel bar in concrete construction. This method includes the steps of: (1) forming a tubular member of a polymeric material having an open end: (2) collapsing an area adjacent an end of the tubular member so as to form a tapered section of narrowing interior diameter; and (3) heat-sealing the opposite end of the tubular member so as to form a closed end of the tubular member. The collapsed end can be formed by compressing the opposite end together by the use of a heated member so that the surfaces at the opposite end are welded together by the heated member. Alternatively, the collapsing of the opposite end can be carried out through a vacuum forming process.